In a conventional seam welder of the resistance type, the welder is conventionally provided with upper and lower weld rolls which function as electrodes and which are relatively urged toward one another so as to permit material to be welded, such as overlapping sheets, to be relatively fed into and through the nip between the opposed weld wheels. The weld wheels directly engage the overlapping sheets and effect compression and electric heating so as to effect both welding and mashing of the overlapping sheets to create what is known as a seam weld.
Referencing FIG. 1, there is illustrated a conventional seam welder 10 wherein there is respectively provided upper and lower weld wheels 11 and 12 respectively supported for rotation about axes 13 and 14, these latter axes extending approximately parallel. The upper and lower weld wheels have their opposed peripheries substantially contacting at the nip 15, and material to be welded is fed into and through this nip. The material to be welded typically employs a pair of sheet metal parts or portions such as illustrated at 16 and 17 in FIG. 2, which portions have an overlapping area or region 18 which is relatively longitudinally fed into the nip so as to permit creation of a seam weld between the overlapping portions. The actual creation of the seam weld and the technology associated with doing so is well known, so that further detailed description of the actual welding steps will not be described in detail.
In the conventional seam welder 10, the upper weld wheel 11 is nonrotatably secured to a rotatable shaft 21 which in turn is rotatably supported within an electrically conductive bearing assembly 22, the latter having a nonrotatable outer housing 23 which has an electrically conductive mounting plate 24 fixed thereto. This conductive mounting plate 24 in turn mounts thereon an electrical insulator 25 which in turn cooperates with a lower end of a vertically reciprocal ram 26, the latter being slidably guided within the stationary machine frame 27. The upper end of ram 26 is acted on by a conventional air pressure cylinder 28 which is appropriately energized by pressurized air so as to impose a downward force on the ram which in turn is transmitted downwardly so as to be imposed on the upper weld wheel 11 and thus on the work located in the nip 15.
The lower weld wheel 12 is also nonrotatably supported on a shaft 31 which is also rotatably supported within an electrically conductive bearing assembly 32, the nonrotatable housing 33 of which also fixedly joins to an electrically conductive plate 34, the latter being stationarily supported on a stationary part 36 of the machine frame through an intermediate electrical insulator 35.
The electrically conductive members or plates 24 and 34 are in turn joined to and supplied with electrical energy from a conventional welding transformer 37 by being respectively connected thereto through flexible conductive straps 38 and 39.
A conventional and known construction of the electrically conductive bearing assembly 22 or 32 is illustrated in FIGS. 6-7. This bearing assembly 22 includes the outer housing 23 which is disposed generally in surrounding relationship to the shaft 21, and this bearing assembly provides seal structure, bearing structure and electrically conductive structure cooperating between the housing 23 and the shaft 21. For example, opposite ends of the elongate housing 23 are normally provided with annular seals 41 to create a sealed relationship between the shaft and the housing bearings 42 such as roller or ball bearings are also typically provided for cooperation between the housing 23 and the shaft 21, which bearings 42 are disposed adjacent opposite axial ends of the housing 23 and are typically positioned axially inwardly from the respectively adjacent seals 41. The housing 23 in addition defines therein an annular chamber 43 of substantial size, which chamber extends axially between the bearings 42 in surrounding relationship to the shaft 21. This chamber 43 contains therein at least one and typically several electrically conductive contact assemblies 44 positioned in axially adjacent relationship for transmitting electrical current from the housing 23 to the rotating shaft 21. In the illustrated arrangement, this contact assembly 44 includes a pair of contact shoes 45 which are disposed in straddling relationship on generally opposite sides of the shaft 21, with these opposed contact shoes 45 typically being constructed of copper and having opposed recesses which are provided with a silver layer 46 thereon, these silver layers 46 in turn being disposed in slidable current-conducting contact with the exterior of the rotatable shaft 21. The contact members 45 themselves are normally urged inwardly into proper contacting engagement with the shaft 21 by appropriate wedges 47 which coat between the contact members and the housing 23, with these wedges 47 typically being acted on by springs 48. The chamber 43 is typically provided with oil, such as castor oil, circulated therethrough for cooling and lubricating purposes.
In the conventional seam welding apparatus as illustrated by FIG. 1, the electrically conductive bearing assemblies such as illustrated at 22 and 32 are typically mounted directly at or axially adjacent the weld wheel or electrode, with the latter being positioned substantially directly adjacent at least one axial end of the bearing assembly, with the upper bearing assembly 22 then being acted on directly by the pressure ram 26 so that the pressing force which acts downwardly through the ram onto the upper weld wheel and thence through the workpiece onto the lower weld wheel is accordingly positioned in close proximity to the work plane, namely the vertical plane containing the weld wheels, so as to maximize the effectiveness of the welding force.
While the overall arrangement briefly described above is desirable with respect to the effective use of the pressing or welding force as imposed between the weld wheels, nevertheless the overall evolution of conductive bearing assemblies as utilized in seam welders of this type has now limited the overall effectiveness and efficiency of seam welders, particularly with respect to their ability to more effectively utilize the welding force and even more specifically with respect to their ability to operate at higher linear speeds (that is, the relative speed at which the work moves through the weld nip). These conductive bearing assemblies as described above and as illustrated by FIGS. 6-7, have evolved so as to typically incorporate silver contact shoes immersed in oil which is part of a recirculating system so that the oil recirculates through the bearing assembly to effect proper lubrication and cooling thereof. This evolution has resulted in conductive bearing assemblies which are more efficient with respect to the bearing function and the electrically conductive function, in that such bearings have been capable of running reliably for one to two years with little or no maintenance. The significant disadvantage of this evolution in conductive bearings, however, is that these conductive bearing assemblies are bulky and heavy, and in fact such conductive bearing assemblies will typically weight between 150 and 500 pounds, depending upon the force and current carrying capability of the bearing assembly. Thus, when such large and heavy conductive bearing assembly is directly coupled to the pressure ram and is located directly at or adjacent the weld roller, such as the vertically movable upper weld roller 11, the total weight of the overall movable assembly including the ram, the bearing assembly and the weld wheel is quite high and in fact typically reaches the point that the welding force which is transmitted through the assembly to the upper weld wheel is unable to adequately respond to the collapse and material thickness variations which exist in the weld nip. The upper weld wheel is thus unable to vertically move and hence respond with the desired speed or frequency so as to maintain adequate weld contact and pressure while enabling the workpiece to be fed through the nip at the desired rate. This nonresponsiveness of the upper weld wheel and the overall heavy assembly defined thereby, in conjunction with the conductive bearing assembly and the moving pressing ram, thus have been observed to limit the speed with which material can be fed into the nip to effect adequate seam welding thereof. In fact, it has been observed that the practical speed for feeding material into and through the nip of the weld wheels in many applications is limited to about 20 feet per minute due to the mass of the bearing assembly 22 and the slow responsiveness of the driving air cylinder 28.
The aforementioned arrangement is further complicated by the fact that the weld wheels 11 and 12 themselves undergo significant wear during continued operation of the seam welder. In fact, it is not uncommon for the diameter of the weld wheel to decrease up to two inches prior to its being replaced, for example a 14 inch diameter weld wheel may wear down to about 12 inches in diameter prior to its being replaced. This significant wear must also be compensated for by the driving cylinder, which is in addition to the rather rapid but small adjustment desired so as to compensate for thickness variations in the workpiece, thus making creation of a quality seam weld while operating at a high linear speed very difficult and in most instances impossible to achieve with the current and preferred construction of the bearing support.
Accordingly, it is an object of this invention to provide an improved bearing support arrangement for the moving weld wheel of a seam welding apparatus, which improved bearing support arrangement is believed to overcome the aforementioned disadvantage and provide for greater and more rapid response of the moving weld wheel to thickness variations in the material being seam welded, while also compensating for weld wheel wear.
More specifically, this invention relates to an improved bearing support arrangement for the transversely movable weld wheel (i.e., the upper weld wheel in the illustrated embodiment) of a seam welding apparatus, which bearing support arrangement is effective in isolating or at least minimizing the effect of the mass of the pressing ram and of the conductive bearing assembly from the transversely movable weld wheel, whereby the weld wheel can more readily follow and respond to thickness variations in the work or material being fed into and through weld nip, thereby optimizing the ability of the pressing system to deliver a more consistent or uniform pressing force through the weld wheel onto the work or materials being welded, and at the same time enabling the work or materials being welded to be fed through the nip at a higher speed or rate, while at the same time permitting creation of an efficient and desirable seam weld on the work or materials. This improved bearing arrangement, as aforesaid, is also supported in such fashion as to permit compensation for significant weld wheel wear, such as significant reduction in diameter, while at the same time still permitting a pressing system to deliver a substantially uniform pressing force for high speed operation while compensating for thickness variations in the work or material being fed through the weld nip.
In the seam welding apparatus of this invention, as incorporating therein the improved bearing support arrangement for the transversely movable weld wheel (i.e., the upper weld wheel in the disclosed and preferred embodiment), the upper weld wheel is nonrotatably secured adjacent one end of an elongate electrically conductive shaft which is supported for rotation, which shaft adjacent its other end is rotatably supported within a conventional electrically conductive bearing assembly which rotatably supports the shaft and transmits electrical energy thereto from an external source such as a transformer. The shaft is of substantial axial length, and the upper weld wheel and electrically conductive bearing assemblies are disposed adjacent opposite ends of the shaft so as to be spaced a significant axial distance from one another. The nonrotatable housing associated with the bearing assembly is in turn pivotally supported on a slide member by a pivot which extends generally through the housing in transverse or perpendicular relation to the shaft axis, with this pivot axis also being disposed adjacent the end of the shaft mounting the bearing assembly so as to be remote from the weld wheel. A welding force generating assembly such as a fluid pressure cylinder and ram are mounted on the machine frame, with the ram being movably supported and acting downwardly onto the slide member to effect sliding displacement thereof in a direction generally perpendicular to the plane of the nip defined between the weld wheels. A spring unit is mounted on the slide member in close proximity to the end of the shaft which mounts the weld wheel. The spring unit has an electrical insulator associated therewith. This spring unit and its electrical insulator are rotatably supportingly engaged with the shaft closely axially adjacent the weld wheel so that the force generated by this unit is applied to the shaft and thence directly onto the weld wheel to create a weld force which is imposed on the work or materials located in the nip. Since the large and massive electrically conductive bearing assembly is located substantially at the remote pivot axis which enables the weld wheel to vertically float up and down in response to work or material thickness variations, the bearing assembly due to its proximity substantially at the pivot axis accordingly generates little inertia, and thus has little or only minimal effect on the vertical displacement of the weld wheel and hence the responsiveness thereof. At the same time the force generating unit still acts directly adjacent or in close proximity to the plane of the weld wheel so as to impose an effective downward welding force onto the upper weld wheel, and the fact that the weld wheel shaft is coupled to the force generating unit through the spring unit, thus also tend to minimize and effectively eliminate most of the inertia of the pressing ram so that the weld wheel can vertically respond to material thickness variations at the nip without having to being impeded in its motion due to the high inertia of the pressing ram and bearing assembly. Since the mass which is now being vertically displaced or cycled in response to material thickness variations has been substantially minimized, the inertia is likewise significantly minimized, and the weld wheel is able to more readily and rapidly respond to material thickness variations. This enables a more effective and uniform weld force to be maintained, and at the same time enables the work or materials as supplied to the nip to be fed therethrough at a higher speed or rate.
Further, since the weld shaft as well as the bearing and pivot support arrangement, as well as the spring unit, are all mounted on a slide member which itself is connected directly to and slidably displaced by the fluid pressure cylinder, the overall support bearing arrangement can in addition readily compensate for the significant reduction in weld wheel diameter, while still readily responding to and compensating for thickness variations in the material being welded so as to permit a seam weld to be created at a rather high speed.
With the improved arrangement of this invention, several advantages are believed provided, more specifically lower welding forces can be used, less current may be required for welding, higher welding speeds are believed obtainable, metal explosion during welding can be reduced or eliminated, larger weldability ranges are obtainable, welding wheel or electrode life is improved, and the pick-up or alloying of coatings during welding of coated materials is reduced.
Other objects and purposes of the invention will be apparent to persons familiar with structures of this general type upon reading the following specification and inspecting the accompanying drawings.